diff --git a/core/modules/block/src/Tests/BlockHiddenRegionTest.php b/core/modules/block/src/Tests/BlockHiddenRegionTest.php
index a6af2ce..bb42dce 100644
--- a/core/modules/block/src/Tests/BlockHiddenRegionTest.php
+++ b/core/modules/block/src/Tests/BlockHiddenRegionTest.php
@@ -56,7 +56,9 @@ public function testBlockNotInHiddenRegion() {
 
     // Install "block_test_theme" and set it as the default theme.
     $theme = 'block_test_theme';
-    \Drupal::service('theme_handler')->install(array($theme));
+    // We need to install a non-hidden theme so that there is more than one
+    // local task.
+    \Drupal::service('theme_handler')->install(array($theme, 'stark'));
     $this->config('system.theme')
       ->set('default', $theme)
       ->save();
diff --git a/core/modules/block/src/Tests/BlockTest.php b/core/modules/block/src/Tests/BlockTest.php
index c98b042..261c3ae 100644
--- a/core/modules/block/src/Tests/BlockTest.php
+++ b/core/modules/block/src/Tests/BlockTest.php
@@ -197,9 +197,9 @@ function testBlock() {
    */
   public function testBlockThemeSelector() {
     // Install all themes.
-    \Drupal::service('theme_handler')->install(array('bartik', 'seven'));
+    \Drupal::service('theme_handler')->install(['bartik', 'seven', 'stark']);
     $theme_settings = $this->config('system.theme');
-    foreach (array('bartik', 'classy', 'seven') as $theme) {
+    foreach (['bartik', 'seven', 'stark'] as $theme) {
       $this->drupalGet('admin/structure/block/list/' . $theme);
       $this->assertTitle(t('Block layout') . ' | Drupal');
       // Select the 'Powered by Drupal' block to be placed.
diff --git a/core/modules/block/tests/src/Unit/Menu/BlockLocalTasksTest.php b/core/modules/block/tests/src/Unit/Menu/BlockLocalTasksTest.php
index f70a57c..6320917 100644
--- a/core/modules/block/tests/src/Unit/Menu/BlockLocalTasksTest.php
+++ b/core/modules/block/tests/src/Unit/Menu/BlockLocalTasksTest.php
@@ -27,7 +27,11 @@ protected function setUp() {
 
     $themes = array();
     $themes['test_a'] = (object) array(
-      'status' => 0,
+      'status' => 1,
+      'info' => array(
+        'name' => 'test_a',
+        'hidden' => TRUE,
+      ),
     );
     $themes['test_b'] = (object) array(
       'status' => 1,
@@ -45,6 +49,13 @@ protected function setUp() {
     $theme_handler->expects($this->any())
       ->method('listInfo')
       ->will($this->returnValue($themes));
+    $theme_handler->expects($this->any())
+      ->method('hasUi')
+      ->willReturnMap([
+        ['test_a', FALSE],
+        ['test_b', TRUE],
+        ['test_c', TRUE],
+      ]);
 
     $container = new ContainerBuilder();
     $container->set('config.factory', $config_factory);
diff --git a/core/modules/block_content/src/Tests/BlockContentTypeTest.php b/core/modules/block_content/src/Tests/BlockContentTypeTest.php
index e669a72..d1405b9 100644
--- a/core/modules/block_content/src/Tests/BlockContentTypeTest.php
+++ b/core/modules/block_content/src/Tests/BlockContentTypeTest.php
@@ -185,17 +185,15 @@ public function testsBlockContentAddTypes() {
       ->getStorage('block_content');
 
     // Install all themes.
-    \Drupal::service('theme_handler')->install(array('bartik', 'seven'));
-    $themes = array('bartik', 'seven', 'classy');
+    \Drupal::service('theme_handler')->install(['bartik', 'seven', 'stark']);
     $theme_settings = $this->config('system.theme');
-    foreach ($themes as $default_theme) {
+    foreach (['bartik', 'seven', 'stark'] as $default_theme) {
       // Change the default theme.
       $theme_settings->set('default', $default_theme)->save();
       \Drupal::service('router.builder')->rebuild();
 
       // For each installed theme, go to its block page and test the redirects.
-      $themes = array('bartik', 'classy', 'seven');
-      foreach ($themes as $theme) {
+      foreach (['bartik', 'seven', 'stark'] as $theme) {
         // Test that adding a block from the 'place blocks' form sends you to the
         // block configure form.
         $path = $theme == $default_theme ? 'admin/structure/block' : "admin/structure/block/list/$theme";